Sliding contact material, sliding contact element and producing method

ABSTRACT

There are disclosed copper-base and/or iron-base contact materials which contain a Pb intermetallic compound dispersedly precipitated therein and which have highly improved sliding properties. Double layered contact elements improved in oil impregnation and lubricity are formed by sinter bonding the above contact materials to an iron-base metal backing, respectively. Economical producing methods for such double layered contact materials are also disclosed. In the copper-base and/or iron-base contact materials, one or more kinds of Pb intermetallic compounds are dispersedly precipitated.

TECHNICAL FIELD

The present invention generally relates to sliding contact materials,sliding contact elements and sliding contact element producing methods,which are directed to achieving improved wear resistance under highersurface pressure conditions and the capability of noise prevention. Moreparticularly, the invention relates to copper-base and/or iron-basesliding contact materials in which a Pb intermetallic compounds isdispersedly precipitated to improve sliding properties and relates todouble layered sliding contact elements produced by sinter-bonding suchsliding contact materials to an iron-base metal backing in an integralfashion thereby improving oil impregnation properties and lubricity. Theinvention also relates to economical methods for producing such doublelayered sliding contact elements. Hereinafter, sliding contact materialsand sliding contact elements are simply referred to as “contactmaterials” and “contact elements”.

BACKGROUND ART

Bronze materials such as Cu—Sn—Pb and lead-bronze materials are commonlyused as materials for copper-base sintered bearings. Such materials areoften integrally bonded to an iron-base metal backing to form a doublelayered sintered contact element such as a track roller provided in thebase carrier of a construction machine.

As bearings used under high surface pressure and low speed conditionssuch as bushings for use in a construction machine, carburized orhigh-frequency-hardened wear-resistant steel bushings are widely known.When used in a construction machine, a bushing is subjected to highsurface pressure and severe lubricating conditions and likely togenerate undesirable abnormal noise during operation. To cope with thisproblem, there are often used high strength brass bushings or theabove-described steel bushings which have undergone lubricating filmcoating treatment. High strength brass bushings are especiallyattractive because of their superior conformability. To prolong theintervals at which grease is fed to a bearing disposed in a constructionmachine etc., there has been proposed a graphite-embedded bearingmaterial (e.g., 500SP produced by OILLESS INC.) that is produced bymachining a high strength brass bushing to have holes and embeddingporous graphite in the holes to be impregnated with oil. For the samepurpose, a sintered metal body containing a large amount of solidlubricant (e.g., the SL alloys produced by TOSHIBA TUNGALOY CO., LTD.)is used.

Japanese Patent Publication (KOKOAI) No. 5-156388 (Japanese PatentPublication (KOKOKU) No. 56-12288) discloses a double layered sinteredcontact element for use under high surface pressure and its producingmethod. This contact element is formed by integrally bonding analuminum-bronze-base sintered contact alloy, in which graphite isdispersed as a solid lubricating component within the range of 3 to 8 wt%, to a steel plate through a bonding layer.

Japanese Patent Publication (KOKAI) No. 3-232905 discloses a doublelayered sintered contact element having superior resistance to high loadand impact. This element comprises (i) a metal backing that is made of asteel plate having a plurality of independent protrusions at its surfaceor steel plate having a series of connected protrusions and a pluralityof independent recesses defined by the respective protrusions and (ii) acopper-base sintered alloy layer that is integrally formed with themetal backing so as to cover the protrusions of the surface and in whichgraphite is dispersed as a lubricating component in an amount of atleast 3 wt %. This copper-base sintered alloy layer is composed of alow-density, high-oil-impregnating alloy region and a high-density,low-oil-impregnating alloy region.

Double layered sintered contact elements having a lead- bronze-base orbronze-base sintered contact layer are versatilely used as a slidingcontact member of good conformability for the aforesaid lower trackroller or engine metal, under low load, high speed and well lubricatingconditions. However, they are inadequate for use as a bushing for aconstruction machine since they are easily worn out or fatigued due tolack of hardness for withstanding the high surface pressure and severelubricating conditions.

When a steel bushing is used as a bushing in a construction machine, itis not fatigued but likely to cause seizure or unpleasant abnormalnoise.

High strength brass contact materials produced by casting aresubstantially free from fatigue and generate little noise, but easilybecome short of lubricity. Therefore, they cannot completely preventnoise generation and are unavoidably susceptible to rapid wear when theyare used in extremely low speed and high load applications such as whenadapted in a construction machine.

Generally, in a high strength brass base contact material formed as asinter contact alloy, the steam pressure of Zn contained is too high tocarry out high density sintering. Therefore, sintering must be carriedout under a pressurized condition when producing a double layeredsintered contact element from such high strength brass contact materialand, in consequence, production cost cannot be reduced.

In the case of steel bushings coated with a lubricating film, formationof a thick lubricating film is generally difficult and expensive and itis therefore apparent that after the lubricating film provided for suchbushings is worn out, abnormal noise and seizure occur, like the case ofordinary steel bushings.

The graphite-embedded high strength brass bushing having moreself-lubricity (e.g., 500SP produced by OILLESS INC.) requires apunching process for making a large number of holes for graphiteembedding as well as a graphite filling process, in order to achievehigh self-lubricity, which significantly increases cost. In many cases,the ratio of holes for graphite is normally restricted to 25 to 30% on abasis of area in view of cost, and therefore they cannot providesatisfactory self-lubricity over a long period of time.

The degree of sintering is a problem for a sintered metal bodycontaining a large amount of known solid lubricant such as graphite, BNand MoS₂ and therefore a pressure sintering means such as a hot press isrequired in order to achieve high density, resulting in increased cost.In addition, since the conventionally used solid lubricant is extremelysoft, even a high-density metal sintered body suffers from highbrittleness.

In the case of the double layered sintered contact element comprising(i) a steel plate serving as a metal backing and having a plurality ofindependent protrusions or a series of connected protrusions on itssurface and (ii) an integral copper-base sintered contact alloy layercontaining at least 3 wt % graphite, the steel plate backing formed intoa specified shape is expensive and it is extremely difficult and costlyto manufacture a metal backing which has protrusions (high-densityportions) for sustaining a bearing load, in an area ratio of 30% ormore.

Additionally, when bending the above material to produce a tubularbushing, bending stress is concentrated on the protrusions of the steelplate which are harder than other areas, so that exfoliation is likelyto occur in the joint interface between the steel plate and thecopper-base sintered contact material and the deformation resistanceoccurring in the bending operation is unevenly distributed in the steelplate. This makes it difficult to uniformly bend the material into atubular shape. In consequence, a lot of machining work is involved inproducing a tubular bushing, and the cost for inspecting the quality ofbonding between the contact material and metal backing of the finalproduct increases.

The invention is directed to overcoming the foregoing problems.Therefore, an object of the invention is to provide copper-base and/oriron-base contact materials in which Pb intermetallic compounds aredispersedly precipitated to achieve highly improved sliding properties.Another object of the invention is to provide double layered contactelements and their economical producing methods, the contact elementsbeing produced by sinter-bonding the above contact materials to aniron-base metal backing in an integral fashion and being improved in oilimpregnation and lubricity.

DISCLOSURE OF THE INVENTION

To achieve the above objects, the invention includes the followingtechnical means.

According to a first aspect of the invention, there are providedcopper-base contact materials and copper-base and/or iron-base sintercontact materials,

which are softer and more conformable than the above-describedconventional steel bushing material, and

which are basically Cu—Pb—Ti alloys and —Mg alloys having high seizureand wear resistance like high strength brass material, which alloyscontain a Pb intermetallic compound dispersedly precipitated therein byvirtue of the presence of Ti or Mg.

In contrast with the conventional lead-bronze base contact materials andiron-base sinter contact materials in which Pb is dispersedlyprecipitated simply as a metal component, the contact material of theinvention contains Pb dispersed in the form of a Pb intermetalliccompound. With this arrangement, the sliding properties of the contactmaterial under high surface pressure and severe lubricating conditionscan be highly improved. Since Pb is dispersedly precipitated in the formof a Pb intermetallic compound, the contact material may contain Pb atleast in the range of from 1 to 30 wt %. This Pb range is wider comparedto the case where Pb is precipitated as a metal.

As counter metallic elements which strongly combine with Pb to form anintermetallic compound, 1A, 2A, 3A, 4A and 6B groups in the periodictable shown in FIG. 1, lanthanides and actinides may be used incombination, but Ti, Mg, Ca, Ba, Zr, Li, Hf, La, Te, Se, Sm arepreferable in view of cost and availability. Besides, Ti, Mg and Zr aremore preferable for the above reason. The same effect can be expectedwhen other elements than the above are used for forming a Pbintermetallic compound.

Although the contents of the above metallic elements can be calculatedfrom the molar ratio of a Pb intermetallic compound such as CaPb₃, theyneeds to be contained in amounts of substantially 0.5 wt % or more.

Accordingly, the bronze-base sinter contact material is especiallyimportant, which is designed to contain Ti and Mg in an amount of 0.5 to10 wt % in order to improve strength, sliding properties and costperformance and to further contain Sn in an amount of 1 to 10 wt % inorder to ensure bonding strength relative to a metal backing andfacilitate sintering operation.

The upper limit of the amount of Ti and Mg is preferably 10 wt % in viewof cost.

Since it is known that the amount of a Pb intermetallic compound whichcontributes to seizure resistance is about 0.5% by volume in the case ofconventional contact materials containing dispersed hard particles, theamount of Pb is preferably 1 wt % or more and the upper limit of Pb ispreferably 30 wt % in view of strength. Taking the environmentalproblems imposed by Pb in the sintering process into account, the amountof Pb should be restricted to 15 wt % or less. Further, copper-basecontact materials containing Ti are known to react to precipitate otherTi intermetallic compounds than the intermetallic compounds of Ti and Pband undergo age hardening. It is also known that the strength andhardness of Ti-containing copper-base contact materials can be improvedby adding alloy elements such as Al, Ni, Si, Fe, Mn, Cr, Be and thelike. In view of these facts, it is appropriate to contain Ti within therange of up to 5 wt % in order not to impair sintering properties.

It is apparent that the addition of the above metallic elements havingthe ability of forming a Pb intermetallic compound enables fining ofCu-base sinter alloy structures and in consequence the uniformdispersion of Pb, providing excellent sliding properties.

The appropriate amount of Ti is 0.5 wt % or more by which a Tiintermetallic compound precipitates and the upper limit of the amount ofTi is preferably 10 wt % in view of cost. For producing a constructionmachine bushing or the like for use under high surface pressures, themore preferable amount of Ti is 2 wt % or more, taking the hardness(Hv=150 or more according to the actual record) of high strength brassbushings into account.

In conventional contact materials containing dispersed hard particles,remarkably stable sliding properties can be admitted when 0.5% by volumeof hard particles are dispersed. Therefore, the amount of Pb is 1 wt %or more and, more preferably, 5 to 10 wt % when converted to a Pbintermetallic compound basis.

It is obvious that the same inventive factors as those of the abovecopper-base sinter contact materials can be achieved by cast materials.Accordingly, the scope of the invention covers the case where a castmaterial is machined and formed into the copper-base contact elementhaving improved sliding properties.

According to the invention, the copper-base contact materials preparedby casting and the copper-base and/or iron-base sintered contactmaterials prepared by sintering may be designed, in consideration of thesurface pressure imposed on these materials during operation and theintervals at which grease is supplied, to have 10 to 70% holes on anarea ratio basis and contain grease or oil impregnated plastics embeddedin the holes. The invention also covers the case where a copper-basesinter material powder which is expandable by sintering is introduced inthe holes of the copper-base and/or iron-base contact materials andsintering is carried out to form a porous sintered body excellent in oilimpregnation so as to be bonded to the contact materials, as disclosedin Japanese Patent Publication (KOKAI) No. 8-291306.

According to a second aspect of the invention, there is provided adouble layered sintered contact element whose outermost sliding surfaceis made of the above-described copper-base sinter contact material. Thisreduces the use of the copper-base sinter contact material therebysaving costs. The double layered sintered contact element contains atleast 1 wt % or more Sn in order to ensure bonding strength between thecontact material and an iron-base metal backing. In order to lowersintering temperature, the preferable amount of Sn should not exceed 10wt %.

The addition of P causes the generation of a liquid phase at lowtemperatures thereby accelerating sintering. To restrict excessivereaction with the iron-base metal backing, the amount of P is preferablyadjusted so as not to exceed 1 wt %.

For bonding to the iron-base metal backing, a powder of the abovecopper-base sinter alloy is sprayed onto the surface of the iron-basemetal backing and sinter bonding is then carried out in a neutral orreducing atmosphere at at least not higher than 890° C. which is theeutectic temperature of Cu—Ti duel alloys. Thereafter, a pressurizingprocess such as rolling is carried out to form a copper-base sinteredlayer having desired density or thickness. Bending may be carried out atthe same time. Then, the material is again sintered in the sameatmosphere described above. The reason why the temperature of the firstsintering operation is restricted to the eutectic temperature (890° C.)of Cu—Ti duel alloys or less is that a Ti compound precipitating at thejoint interface between the contact material and the iron-base metalbacking is restricted to thereby restrain the occurrence of exfoliationat the joint interface during the subsequent process of bending. Wherethe bending process is incorporated, the temperature of the secondsintering operation is preferably 950° C. or less. Where thepressurizing process for density adjustment is carried out without thebending process, the preferable second sintering temperature is 890° C.or less and it is preferable to carry out sintering again at the targettemperature of 950° C. or less after the second sintering operation.

Where a compact sheet which has undergone rolling or press molding isset on the iron-base metal backing for sintering, it is preferable thatafter sintering at a temperature of 890° C. or less, the compositematerial be bent and sintered again. The reason for this is that theprecipitation of a Ti compound at the joint interface is restricted toprevent exfoliation as stated earlier.

According to a third aspect of the invention, when forming a doublelayered sintered contact element by integrally bonding the copper-basecontact material containing Ti and Pb to the iron-base metal backing, asintered insert layer may be interposed between them. With the provisionof the sintered insert layer, the precipitation of the aforesaidcompound at the joint interface can be further prevented in the bendingprocess thereby increasing plastic deformability. As a result, thenumber of sintering operations can be reduced to increase productivity.In addition, not only improved bonding quality but also cost savings canbe achieved.

The copper-base contact material used in the above double layeredsintered contact element having the sintered insert layer may be a castmaterial or sinter contact material. As described earlier, it isapparent that a copper-base contact element having 10 to 70% holes on anarea ratio basis can be produced at low cost. Additionally, the contactmaterial, which has holes containing the above expansive copper-basesinter material sinter-bonded thereto, may be integrally adhered to themetal backing with the sintered insert layer between. This enables aninexpensive, double layered sinter-bonded contact element.

According to a forth aspect of the invention, the above-describedsintered insert layer may be formed from an iron-base sinter material,thereby markedly reducing the cost of the material of the sinteredinsert layer. A preferable iron alloy used for making the sinteredinsert layer contains (i) an iron or iron alloy powder made by thereduction and/or atomizing method commonly used in ordinary metallurgy,as a major component; (ii) at least 20 to 60 wt % copper; and (iii) 2 to7 wt % Sn. The iron alloy for the sintered insert layer preferablycontains a component which generates a liquid phase having alower-meting point such as Pb and P.

It should be noted that when the iron alloy for the sintered insertlayer is sprayed onto the metal backing and then sinter bonding iscarried out in the temperature range of 890° C. or less, not significantcompaction but a slight amount of expansion is admitted and thestructure after sintering has many voids formed by linked iron-basepowder particles, resulting in a low apparent density. Where a bronze orphosphor-bronze sinter alloy is used for the sintered insert layer, thedegree of sintering rapidly increases from 800° C. or more and the alloyis melted at an adequate sintering temperature for the copper-basesinter contact alloy of the invention containing Ti and a large amountof Pb, or the copper-base sinter contact material is significantlyalloyed with the insert layer material so that the quality of thesliding contact layer cannot be controlled. For this reason, the aboveiron-base sinter material is used for the insert layer of the invention.

In addition, since the surface of the iron-base sintered insert layer isrough, when spraying a mixed powder of the copper-base sinter contactmaterial onto the iron-base insert layer, spraying can be easilycontrolled so as to vary the thickness of the contact material layer.Where the thickness of the contact material layer is less than 0.5 mm,rolling can be directly performed after the spraying operation andtherefore sintering can be advantageously successively carried out inthe next process. This contributes to cost savings in the production ofthe double layered sintered contact element. Where the above thicknessis 0.5 mm or more, such direct rolling after the spraying operationcannot be carried out and therefore it is preferable to carry out apressing operation such as rolling during re-sintering to adjust thedensity and thickness of the material.

In the case of the double layered sintered contact element produced inthe way described above, since the deformation resistance of thecopper-base sinter contact material is much smaller than that of theiron-base insert layer material, the surface contact layer has highdensity and strength while the iron-base sintered insert layer can bemade porous so that the resultant double layered sintered contactelement has superior oil impregnation properties.

According to a fifth aspect of the invention, the porous sintered insertlayer, which has been adjusted in thickness and bonded to a steel plate,is machined so as to be rugged and after the copper-base contactmaterial is sprayed to the machined surface, rolling and re-sinteringare carried out, whereby a low-cost double layered sintered contactelement having low-density, high-oil-impregnation regions andhigh-density, low-oil-impregnation regions at the sintered contact layercan be obtained.

This material is intended for further enhancing the advantageous feature(i.e., porosity) of the above iron-base sintered insert layer. Bymachining the iron-base sintered insert layer to have convex portionsand concave portions and spraying a mixed powder of the sinter contactmaterial onto the rugged surface, the independent or linked concaveportions are filled with a comparatively large amount of the contactmaterial powder while the convex portions are slightly covered with thecontact material powder. Then, rolling for obtaining a specified densityor thickness is successively carried out like the above case andsintering is then carried out at 950° C. or less so that the doublelayered sintered contact element can be easily produced. This processfor producing the double layered sintered contact element may bealternatively arranged such that, after a powder of the sintered contactmaterial is sprayed onto the rugged surface, sintering is once carriedout at 890° C. or less and followed by rolling for density and/orthickness adjustment and thereafter sintering is again carried out.

According to a six aspect of the invention, a mixed powder of the abovecopper-base and/or iron-base sinter contact material is compacted withina die under a specified pressure to form a tubular green compact; thisgreen compact is inserted into a tubular iron-base metal backing; andsinter bonding is carried out to integrally form a double layeredsintered contact element.

As described above, the inventors have developed a copper-base sintercontact material in which a Pb intermetallic compound is dispersed inthe base and which contains Ti and Mg, thereby achieving a sintercontact material which has superior seizure resistance and more abilityfor withstanding wearing sliding conditions under high surface pressure,compared to the conventional high strength brass contact material andiron-base contact material, and which, further, has the capability ofrestraining abnormal noise even under severe lubricating conditions. Theinventors also have developed a double layered sintered contact elementformed from the above sinter contact material thereby achieving alow-cost sliding contact element having the aforesaid excellentfeatures. Further, the inventors propose the provision of an iron-baseinsert layer between the above-described sinter contact material and aniron-base metal backing as well as the provision of low-densityhigh-oil-impregnation copper-base sintered contact regions andhigh-density low-oil-impregnation copper-base sintered contact regionson the iron-base insert layer by making the surface of the insert layerrugged. With this arrangement, oil content can be increased and feedingof a lubricant to the high-density low-oil-impregnation copper-basesintered contact regions subjected to more severe lubricating conditionsis facilitated to thereby achieve a highly seizure-resistant, low-costdouble layered sintered contact element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a periodic table of Pb intermetallic compounds.

FIGS. 2a-2 c shows microphotographs of metallographic structures eachtaken at an area close to the joint interface of an alloy and a metalbacking.

FIG. 3 is a sectional view of a specimen used in a sliding test.

FIG. 4(a) is a conceptual view of a tester and FIG. 4(b) shows testconditions.

FIG. 5 shows the result of a sliding test conducted on each bushing.

FIG. 6 illustrates a process for producing a double layered sinteredcontact element having an insert layer.

FIG. 7 shows a microphotograph of the metallographic structure of adouble layered sintered contact member having an iron-base sinteredinsert layer made of alloy sample No. 22.

FIG. 8 diagrammatically illustrates how the surface of a sinter bondedinsert layer coarsens.

FIGS. 9(a) to 9(d) show a process of producing a double layered sinteredcontact element having an insert layer.

FIG. 10 shows the result of a sliding test conducted on a double layeredsintered contact element having an iron-base insert layer.

FIG. 11 shows one example of contact elements subjected to punching.

FIG. 12 shows the result of a sliding test conducted on each bushing.

FIGS. 13(a) to 13(g) show a process of producing a double layeredsintered contact element in which a steel pipe is used as a metalbacking.

FIG. 14 is a microphotograph showing the metallographic structure of adouble layered sintered contact element prepared in Embodiment 5.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the accompanying drawings, the contact materials,contact elements and contact element producing methods of the inventionwill be concretely described according to embodiments.

(Embodiment 1)

1) Development of copper-base sinter contact materials in which a Pbintermetallic compound is dispersedly precipitated

TABLE 1 shows the compositions of copper-base sinter contact materialsused in this embodiment and comparative materials. The materials of theinvention were prepared in the following process. Mixed powders wereprepared using an electrolytic copper powder (CE15), an LBC alloyatomized powder (Cu-10Sn-10Pb), a Cu-33Sn atomized powder, a Mg stampedpowder, a Sn atomized powder, a Pb atomized powder, an Al atomizedpowder, a Cu-50wt % Pb alloy atomized powder, TiH, SiO₂, phosphor iron(27 wt % P), a carbonyl Ni powder, a NiAl stamped powder, and a Sistamped powder. These mixed powders were respectively sprayed onto aS45C steel plate having a thickness of 5 mm, width of 150 mm and lengthof 1,000 mm and slightly ground with sand paper, so that a 10 mm-thicklayer of each mixed powder was formed. These plates were then sinterbonded at 850 to 930° C. within a sintering furnace in an atmosphere ofAX gas having a dew point of −35° C. or less. After the sprayed powderlayer of each material was rolled into 3.0 mm, re-sintering was carriedout at the same temperature, i.e., 850 to 930° C., thereby preparing adouble layered sintered contact element.

TABLE 1 COMPOSITIONS FOR ALLOYS No Cu Ti Mg Pb Sn Cu8P Ni NiAl Si Fe 1Bal 3 — 3 8 — — — — 2 Bal 6 5 2 3 Bal 10 5 2 4 Bal 6 10  2 5 Bal 6 5 26.25 6 Bal 6 5 4 5 7 Bal 6 5 4 3 8 Bal 6 5 4 2 9 Bal 6 10  10  10  Bal0.5 3 5 5 11  40 2 3 6 Bal 12  40 3 6 Bal COMPARATIVE SAMPLE 1 Bal — — —10  6.25 — — — — COMPARATIVE SAMPLE 2 Bal — — 10  10  — — — — —COMPARATIVE SAMPLE 3 HIGH STRENGTH BRASS (P31H PRODUCED BY CHUETSU METALWORKS CO., LTD.) COMPARATIVE SAMPLE 4 SCR420H(C: 0.2, Cr: 0.9, Mn: 0.7,Si: 0.24, Fe: Bal)

TABLE 2 shows the exfoliation states of the sintered layers of tubularbushings which were made from the contact materials listed in TABLE 1through the following process. After each material was sinter bonded ateach sinter bonding temperature shown in TABLE 2 and the sprayed powderlayer was rolled into 3 mm as described above, re-sintering was carriedout at the same sintering temperature to form a blank. Then, bending wasperformed to form a tubular bushing having a bore of 50 mm and length of60 mm. To obtain each result, 20 samples were checked. As seen fromTABLE 2, the sintered layers of the bushings sintered at 910° C. weresignificantly exfoliated.

TABLE 2 SINTERING TEMPERATURE No 850° C. 870° C. 885° C. 910° C. 930° C.1 ◯ ◯ ◯ Δ* × 2 Δ* ◯ ◯ × × 3 Δ* ◯ ◯ × — 4 ◯ ◯ ◯ × — 5 ◯ ◯ Δ* × — 6 Δ* ◯ ◯× — 7 ◯ ◯ ◯ × — 8 ◯ ◯ ◯ × — 9 ◯ ◯ ◯ × — 10 ◯ ◯ ◯ — — COMPARATIVE ◯ ◯FOAMED — — SAMPLE 1 COMPARATIVE ◯ FOAMED FOAMED — — SAMPLE 2 Δ*: PARTIALEXFOLIATION DUE TO A SHORTAGE OF LIQUID PHASE ◯: NO EXFOLIATION ×:EXFOLIATION

FIGS. 2(a) and 2(b) microscopically shows the structure of alloy sampleNo. 2 listed in TABLE 1 in the vicinity of the joint interface with themetal backing when the alloy was sintered twice at temperatures of 885°C. and 910° C. FIG. 2(c) also shows the structure of alloy sample No. 9in the vicinity of the joint interface with the metal backing when thealloy was sintered once at 870° C. It is understood from the result ofalloy sample No. 2 that when an alloy liable to exfoliation is used, aTi intermetallic compound is precipitated in the joint interface andthis precipitation is a cause to the exfoliation at the joint interface.It is preferable to apply a bending process to a material in such acondition that a Ti intermetallic compound at about 890° C. or less islinked to the joint interface without precipitating. When a materialhaving large amounts of Sn and Pb like alloy sample No. 9 is used, theliquid phase is generated in a considerable amount even inlow-temperature sinter bonding at 850° C. Therefore, the materialbecomes highly dense in the first sinter bonding and, in some cases, inspite of the structure in which a Ti intermetallic compound isdispersed, the Ti intermetallic compound linked to the joint interfaceis not precipitated. It is understood from this fact that where Sn andPb generate a large amount of liquid phase at lower temperatures insinter bonding before Ti directly concerns with the liquid phasereaction, the precipitation of a Ti intermetallic compound linked to thejoint interface between the contact material and the metal backing canbe prevented.

When sintering alloy sample No. 2 at 890° C. or less, Ti powder is oftenalloyed insufficiently as seen FIG. 2(a) and the sliding properties ofthe material in this condition are undesirable for the reason explainedlater. Therefore, re-sintering is needed for sufficiently alloying Tiafter the bending process in order to achieve improvements in seizureresistance due to a Pb intermetallic compound and in wear resistance dueto the precipitation of a Ti intermetallic compound. Thus, whenproducing a tubular double layered sintered contact element, it isnecessary to perform sintering after the bending process to precipitatea Ti intermetallic compound.

The same process as applied to the alloy samples of the invention wasapplied to comparative samples 1 and 2 at a sinter bonding temperatureof 850° C. without carrying out re-sintering during the bending process.These samples then underwent the following sliding test.

The configuration of the specimens used in the sliding test is shown inFIG. 3. The specimens have oil grooves in their bores. The conceptualview of the tester and the test conditions are shown in FIG. 4. Forpreparing a specimen, each sample was sinter bonded at 870° C. and thenrolled. Subsequently, the second sintering was carried out at 870° C.and followed by a bending process. After the third sintering at 910° C.,machining was carried out to obtain the configuration shown in FIG. 3.In the test, the oil grooves formed on the inner face of each bushingspecimen were filled with lithium grease and the sliding surface wasthin coated with lithium grease. After the bushing specimen was mountedon the tester, project surface pressure was raised by 100 kg/cm² untilit reaches 800 kg/cm², while the bushing specimen was reciprocated in asliding motion 1,000 times for every 100 kg/cm² rise in project surfacepressure. When the specimen was seized causing a rapid increase in thecoefficient of friction or when abnormal wear or abnormal noiseoccurred, the test was interrupted for evaluation.

FIG. 5 shows the surface pressures which the respective bushingspecimens could sustain. It is obvious from the comparison that thebushings prepared according to the invention are superior to thebushings of the comparative samples. The carburized bushing run out oflubricant and generated abnormal noise from the time when the surfacepressure reached 200 kg/cm². Comparative sample No. 3 of high strengthbrass generated abnormal noise under a surface pressure of 400 kg/cm²and comparative samples Nos. 1 and 2 caused abnormal wear under asurface pressure of 300 kg/cm².

The bushing sample, in which TiH powder remained in shape withoutforming an enough amount of a Ti intermetallic compound when sintered at885° C. or less, also generated abnormal noise and started to seizeunder a surface pressure of 300 kg/cm² (marked with ♦ in FIG. 5).

The bushing formed from sample No. 10 containing Mg (sinteringtemperature=850° C.) exhibited sliding properties as good as those ofthe samples containing Ti from which it is understood that Mg has aneffect common to alloy elements having the capability of forming a Pbintermetallic compound.

Double layered bushings formed by sintering the Fe-base sinter contactmaterials Nos. 11 and 12 containing Cu, Sn, Pb and Mg (preliminarysintering temperature and sintering temperature are both 880° C.) weretested. The Fe-base sinter contact materials proved to have effectssimilar to those of copper-base sinter contact materials, but in orderto exert such effects, the Fe phase region susceptible to seizure shouldbe sufficiently cut off by the copper phase region and therefore thevolume of the Fe phase region in Fe-base materials is restricted to atleast 60% by volume or less.

(Embodiment 2)

2) Development of a double layered sintered contact element having aninsert layer

TABLE 3 shows the compositions of alloy materials used for forminginsert layers according to this embodiment. For preparing the mixedpowders, KIP255 (a reduced iron powder produced by KAWASAKI STEELCORPORATION), a Cu 25 wt % Pb atomized powder and the above raw materialpowders were used. As shown in FIG. 6, the mixed powders 10 (materialsfor an insert layer) of samples Nos. 21 to 24 were sprayed ontorespective metal backings 11 to respectively form an insert layer ofabout 2 mm in thickness and then sinter bonded at 850 to 880° C. Afterthat, the mixed powders 12 of the copper-base sinter contact materialsNos. 2 and 5 were sprayed onto the respective insert layers therebyrespectively forming a 4 mm-thick layer. After re-sintering at 910° C.,each composite material was rolled and bent into a tubular shape,thereby forming a bushing. It has been found that the possibleexfoliation of the insert layer and the copper-base sintered contactmaterial in the bending process can be completely prevented. Inaddition, the process of this embodiment is shorter than the doublelayered sintered contact element (bushing) fabrication process by sinterbonding each of the copper-base sinter contact materials described aboveto a metal backing, and cost savings can be achieved by the use of aniron-base alloy for a sintered insert layer. As reference, themetallographic structure of a contact element having a sintered insertlayer is shown in FIG. 7.

TABLE 3 COMPOSITIONS FOR ALLOYS FOR INSERT LAYER (WT %) No KIP255 Cu PbSn P 21 Bal 15 10 3 22 Bal 30 3 5 23 Bal 30 10 5 24 Bal 10 0.5* *Fe27PIS USED

FIG. 8 diagrammatically shows how the surface of the sinter bondedinsert layer coarsens considerably. The copper-base sinter contactmaterial powder sprayed over the insert layer falls in the large voidsso that the powder is prevented from escaping during the rollingprocess. This makes it possible to carry out the above-described directrolling just after spraying the copper-base sinter contact materialmixed powder onto the sintered insert layer. In this embodiment, thethickness of the copper-base contact material layer which enables directrolling was checked. In this check, the metal powders used for preparingthe copper-base sinter contact material powders were atomized powdersexcept TiH. As a result, it was found that the suitable thickness of thecopper-base contact material layer after sintering was approximately 1.0mm.

In cases where a thicker layer of a copper-base sinter contact materialis formed, there are difficulties in performing the above direct rollingand therefore re-sintering, rolling and roll-bending need to be carriedafter spraying of the copper-base sinter contact material onto theinsert layer.

(Embodiment 3)

3) Development of a density division type doubled-layered sinteredcontact element having an insert layer

More adequate double layered sintered contact elements can be developedby using Pb containing iron-base sinter contact materials (such as alloysamples Nos. 21, 22, 23 of TABLE 3) as an iron-base sinter material foran insert layer. Such Pb containing iron-base materials have better wearresistance under low-speed, high-load conditions, compared to LBC sintercontact materials.

The fabrication process of this embodiment is similar to theabove-described process for fabricating the iron-base insert layer.Specifically, the process of this embodiment comprises, as shown in FIG.9, the following steps: (a) a mixed powder is sprayed to a metal backing11 to form an 8-mm thick insert layer and then sinter bonded at 880° C.;(b) convex portions and concave portions (i.e., ruggedness) are formedby pressure molding; (c) a copper-base sinter contact material powder 12is sprayed onto the insert layer 13 such that the concave portions arefilled with larger amounts of the copper-base sinter contact materialpowder 12 (d) rolling, sintering at 910° C. and bending are sequentiallycarried out. In this double layered sintered contact element, highdensity regions are formed from the above copper-base sinter contactmaterial having excellent sliding properties while low density regionsare formed from the iron-base insert sinter contact material and/or thincovered with the above copper-base sinter contact material. Since thiselement has high oil content, the high density regions which have tosustain most of load are effectively lubricated. In addition, the use ofthe above, expensive, copper-base sinter contact materials can bedramatically reduced and the fabricating process can be simplified,which, in consequence, leads to significant cost savings.

The sliding property of the double layered sintered contact elementaccording to Embodiment 3 was checked in comparison with the element ofEmbodiment 1, by the same sliding test as described earlier. The elementof Embodiment 3 was prepared by using the copper-base contact materialNo. 5 and the iron-base insert material No. 21 while the element ofEmbodiment 1 was prepared by use of the copper-base contact material No.5. The result is shown in FIG. 10 from which it is understood that thebushing of Embodiment 3 having the low density sintered regions isimproved over the bushing of Embodiment 1 in surface pressureresistance.

(Embodiment 4)

4) Development of a double layered sinter bonded contact element havingan insert layer

Alloy sample No. 2 shown in TABLE 1 was high-frequency melted in anatmosphere of Ar gas and then cast in a die to form a cast copper-basecontact element having a thickness of 1.0 mm, width of 70 mm and lengthof 300 mm. This cast material was sinter bonded to a metal backingthrough a sintered insert layer, similarly to Embodiment 2. As thematerial for the sintered insert layer, samples Nos. 22 and 24 (seeTABLE 3) were respectively used.

The fabrication process will be more concretely described. Each powdermaterial for a sintered insert layer was sprayed onto the metal backingto form a layer of 2.0 mm in thickness and then preliminary sinteringwas carried out in the AX gas furnace. The preliminary sinteringtemperatures for samples Nos. 22 and 24 were 850° C. and 830° C.,respectively. After preliminary sintering, the material was rolledthereby preparing a composite body having a 0.7 mm-thick sintered insertlayer. Another composite body was prepared by spraying a Cu-10Pb-10Snatomized powder of #300 mesh under onto the preliminary sintered insertlayer, smoothing the surface to form a layer of 0.1 mm, and then rollingthe material to obtain an insert layer having a thickness of 0.7 mm.Then, the above cast copper-base contact material was placed on andsinter bonded to the respective composite bodies at 880° C.Subsequently, bending was carried out similarly to Embodiment 1 to formtubular bushings. The exfoliation of these tubular bushings was checkedand all the bushings were found to be in good bonding conditions withoutexfoliation at the joint between the contact materials and the backings.When the bonding condition of each bushing was checked by ultrasonicflaw detection, it was found that the bushing prepared by sprayingCu-10Pb-10Sn powder had less defects so that this method is preferableto the other.

The cast copper-base contact material punched so as to have holes asshown in FIG. 11 was placed on an insert layer made of sample No. 22,and the holes were filled with a Cu-1Al-10Sn-5Pb mixed powder. Aftersinter bonding was carried out at 880° C. like the above case, bendingwas carried out to form a tubular bushing. This bushing was checked interms of the quality of bonding between the contact material and themetal backing and in terms of the bonding condition of the poroussintered body formed within the holes, and good results were obtained.

The same sliding test as made in Embodiment 1 was conducted on eachbushing. FIG. 12 shows the test result. Oil grooves were not formed inthe cast contact element provided with holes but it proved to haveexcellent properties by virtue of the lubricating effect of oilimpregnated porous body embedded in the holes.

The contact element shown in FIG. 11, to which a punching metal process(hole making process) has been applied, has excellent performancenotwithstanding that it has not undergone a grooving process. This isobviously attributable to the oil impregnating effect of the poroussintered body sinter-bonded to the holes. It is also obvious that suchgood performance can be ensured even when the contact element is formedwithout integrally bonding a metal backing.

In addition, in the case where the porous sintered body is formed bysinter bonding in the holes made by the punching metal process, thisarrangement has the significant effect of preventing the possibleirregular deformation of the contact material when bent into a tubularbushing, and as a result, the percent defective in the fabrication ofbushings can be decreased and the costs of the subsequent processes canbe saved.

(Embodiment 5)

5) A method for producing a double layered sintered contact elementusing an iron-base pipe material as a metal backing

As shown in FIGS. 13(a) to 13(g), a mixed powder 20 having the samecomposition as sample No. 7 shown in TABLE 1 is molded into a tubulargreen compact body 24 under a pressure of 3 t to 7 t/cm² within amolding unit composed of a punch 21, die 22 and center core 23. Then,the tubular green compact body 24 is inserted into an iron-base pipe 25.At that time, the clearance between the iron-base pipe 25 and thetubular green compact body 24 is 0.2 to 0.5 mm. Thereafter, thecomposite body of the iron-base pipe 25 and the tubular green compactbody 24 is held within a heating furnace under an atmosphere of ammoniacracked gas (dew point=−40° C.) at a temperature of 910° C. for 60minutes and then cooled by gas, so that the expansion behavior of themixed powder containing a Cu—Sn alloy is promoted, increasing thebonding strength of the mixed powder 20 with respect to the iron-basepipe 25. By holding the composite body in a cooled condition, the stateof the mixed powder 20 changes from the expansion behavior to acontraction behavior so that the tubular green compact body 24 iscompacted and diffusion bonded to the inside of the iron-base pipe 25.In this way, a double layered sintered contact element 26 composed ofthe pipe material and the sintered layer integrally bonded to each othercan be obtained.

FIG. 14 shows a microphotograph of the metallographic structure of theabove double layered sintered contact element. As seen from thisphotograph, the quality of bonding between the contact material and theiron-base pipe material serving as a metal backing is good.

A sliding test on the above tubular element was conducted using thetester shown in FIG. 4 and it was found that the tubular element hadsliding properties as good as those of the contact elements having aniron-base metal backing. The iron-base pipe material described hereinincludes sintered pipe material, steel pipe material and cast pipematerial.

What is claimed is:
 1. A sliding contact material which is a copper-baseand/or iron-base contact material and contains one or more Pbintermetallic compounds dispersed and precipitated therein, wherein a Pbintermetallic compound and/or a copper alloy or copper-base infiltratingmaterial which forms a Pb intermetallic compound is infiltrated in aniron-base sintered material.
 2. A sliding contact material according toclaim 1, containing one or more metallic elements which react with Pb,forming a Pb intermetallic compound and are selected from the 1A to 4Agroups and 6B group of the periodic system, lanthanides, and actinides.3. A sliding contact material according to claim 2, containing 1 to 30wt% Pb and 0.5 to 10wt % one or more elements selected from the groupconsisting of Ti, Mg, Ca, Ba, Zr, La, Li, Se and Te which are likely toform an intermetallic compound with Pb.
 4. A sliding contact materialaccording to claim 3, which is a copper-base contact material andfurther comprises a material selected from the group consisting of Sn,Pb, Zn, Al, Si, P, Fe, Be, Ag, Mn and Cr.
 5. A sliding contact materialaccording to claim 3, containing at least 15 to 60wt % Cu 1 to 10wt % Snand the balance iron.
 6. A sliding contact material according to claim3, which is composed of a copper alloy which is formed by expanding acopper-base sinter contact material powder so as to be bonded to aniron-base material and then contracting the copper-base sinter contactmaterial.
 7. A sliding contact element which is a copper-base contactelement, copper-base sintered contact element or iron-base sinteredcontact element, formed from the contact material set forth in claim 4or 5, and having 10-70% of a surface area of the contact elementcontaining holes wherein said holes are filled with a bronze-base sintermixed powder which is expandable by sintering and prepared by mixing atleast one element selected from Al, Si and Cr in the form of a metaland/or alloy powder, and then sintering said mixed powder to form aporous sintered body having a porosity of 20 to 70% by volume and bondedto portions of the contact element defining the holes.
 8. A doublelayered sintered contact element according to claim 7, wherein saidholes are used as oil grooves or filled with an oil impregnating plasticor solid lubricant, thereby enabling oil feeding or self lubricationwhile the contact element is operated in a sliding motion.
 9. A doublelayered sintered contact element formed from the contact material setforth in claim 4 or 5, which contains Sn in an amount of 1 to 10wt % andincludes an integral iron-base metal backing.
 10. A double layeredsintered contact element which is a copper-base sintered contact elementor iron-base sintered contact element, formed from the contact materialset forth in claim 4 or 5, and having 10-70% of a surface area of thecontact element containing holes, wherein said holes are filled with abronze-base sinter mixed powder which is expandable by sintering andprepared by mixing at least one element selected from Al, Si and Cr inthe form of one of a metal and an alloy powder, and then sintering saidmixed powder to form a porous sintered body having a porosity of 20 to70% by volume and bonded to portions of the contact element defining theholes, so that the contact material is made integral with an iron-basemetal backing through a sintered insert layer.
 11. A double layeredsintered contact element according to claim 10, wherein said holes areused as oil grooves or filled with an oil impregnating plastic or solidlubricant, thereby enabling oil feeding or self lubrication while thecontact element is operated in a sliding motion.
 12. A double layeredsintered contact element according to claim 10, wherein after a materialfor forming the sintered insert layer has been preliminarily sinterbonded to the iron-base metal backing, forming a preliminary sinteredlayer, the surface of the preliminary sinter layer is made rugged and apowder of said copper-base and/or iron-base contact material is sprayedonto the rugged surface, and then, a rolling and re-sintering process ora re-sintering and rolling process is applied, whereby high densityregions and low density regions are formed on the sintered contact layerof the resultant double layered sintered contact element to a achievehigh oil impregnation.
 13. A double layered sintered contact element,which is a copper-base sintered contact element or iron-base sinteredcontact element , formed from the contact material set forth in claim 4or 5, and which is formed by preparing a tubular green compact body fromsaid contact material; inserting the tubular green compact body into atubular iron-base metal backing; heating the tubular green compact bodyfor a specified time so as to expand, being bonded to the tubulariron-base metal backing; and further heating the tubular green compactbody to be integral with the tubular iron-base metal backing.
 14. Adouble layered sintered contact element formed from a contact material,which contains Sn in an amount of 1 to 10wt % and includes an integraliron-base metal backing, said contact material being a copper-baseand/or iron-base contact material and contains one or more Pbintermetallic compounds dispersed and precipitated therein, one or moremetallic elements which react with Pb, forming a Pb intermetalliccompound and are selected from the 1A to 4A groups and 6B group of theperiodic system, lanthanides, and actinides, and 1 to 30wt % Pb and 0.5to 10wt % one or more elements selected from the group consisting of Ti,Mg, Ca, Ba, Zr, La, Li, Se and Te which are likely to form anintermetallic compound with Pb, said contact material being acopper-base contact material and further comprises a material selectedfrom the group consisting of Sn, Pb, Zn, Al, Si, P, Fe, Be, Ag, Mn andCr, said double layered sintered contact element further including anintegral sintered insert layer interposed between the contact materialand the iron-base metal backing.
 15. A double layered sintered contactelement formed from a contact material, which contains Sn in an amountof 1 to 10wt % and includes an integral iron-base metal backing, saidcontact material being a copper-base and/or iron-base contact materialand contains one or more Pb intermetallic compounds dispersed andprecipitated therein, one or more metallic elements which react with Pb,forming a Pb intermetallic compound and are selected from the 1A to 4Agroups and 6B group of the periodic system, lanthanides, and actinides,and 1 to 30wt % Pb and 0.5 to 10wt % one or more elements selected fromthe group consisting of Ti, Mg, Ca, Ba, Zr, La, Li, Se and Te which arelikely to form an intermetallic compound with Pb, said contact materialbeing an iron-base contact material and contains iron as a majorcomponent, at least 15 to 60 wt % Cu and 1 to 10wt % Sn, said doublelayered sintered contact element further including an integral sinteredinsert layer interposed between the contact material and the iron-basemetal backing.
 16. A double layered sintered contact element accordingto claim 14 or 15 wherein after a material for forming the sinteredinsert layer has been preliminarily sinter bonded to the iron-base metalbacking, forming a preliminary sintered layer, the surface of thepreliminary sinter layer is made rugged and a powder of said copper-baseand/or iron-base contact material is sprayed onto the rugged surface,and then, a rolling and re-sintering process or a re-sintering androlling process is applied, whereby high density regions and low densityregions are formed on the sintered contact layer of the resultant doublelayered sintered contact element to achieve high oil impregnation.